Retracting rail clamp

ABSTRACT

A retracting rail clamp for braking or anchoring a rail-mounted machine such as a crane by clamping opposite sides of a longitudinal rail member, the retracting rail clamp comprising: a load transfer frame rigidly secured to the crane, such as by bolting; and a clamp mechanism suspended within the load transfer frame by at least one lateral pair of pivotally mounted lift levers, and operable through a first and second stage of motion between a raised, brake release position, in which the entirety of the rail clamp is disposed substantially vertically clear of the rail, and a lowered, brake set position wherein at least one opposed facing pair of main levers of the clamp mechanism engage the side surfaces of the rail.

TECHNICAL FIELD

In embodiments of the presently disclosed subject matter, there isprovided a retracting rail clamp for braking or anchoring a rail-mountedmachine such as a crane by clamping opposite sides of a longitudinalrail member.

BACKGROUND

Rail clamps, also sometimes referred to as storm brakes, are generallyknown in the art. By way of example, U.S. Pat. No. 3,972,392 to Johnson,issued 3 Aug. 1976, discloses a clamping apparatus adapted to grip thesides of rails in a fail-safe mode of operation, thereby to secure anunpowered or unattended crane to its rails and resist external forcestending to move the crane along the rails. Johnson teaches that afail-safe clamping apparatus adapted to clamp the sides of crane railsshould satisfy several requirements. First, it should be independentlypowered by fail-safe means such that it is actuated when the crane isunpowered or unattended; second, the clamping assembly should permitsufficient lateral movement of the clamp with respect to the rail toaccommodate the movement of the crane wheels on the rail as limited bythe tread width between the wheel flanges; third, lateral movement ofthe clamp assembly should not significantly alter the angle at which theclamping surfaces approach the sides of the crane rails; fourth, wherethe clamping surfaces comprise metal serrated shoes of hardnesssubstantially greater than that of the rail, means should be provided toprevent the shoes from dragging on the rails when the crane moves alongits rails; fifth, the clamping assembly should be of narrow crosssection such that the opening in a traveled surface in which the railsare embedded, as in the case of a dock facility, does not exceedapproximately three times the width of the top of the rail; and finally,means should be provided whereby remote sensing means are provided toindicate to the crane operator that the clamp is fully released prior tomovement of the crane on its rails. Johnson provides a fail-safeclamping apparatus wherein its clamping surfaces are externally mountedto facilitate periodic examination without disassembling the clampingassembly.

U.S. Pat. No. 7,975,811 to Berliant, issued 12 Jul. 2011, discloses aconstant force rail clamp having a frame and a pair of levers. Each ofthe levers has a brake pad at a first end thereof, a cam follower atsecond end thereof, and is mounted to the frame by a pivot disposedbetween said first and second ends. A cam is disposed between the leversand a spring biases the cam in a first direction. A clamp releaseactuator is operable to displace the cam in a second direction, which isopposite to the first direction. A pair of variably sloped cam surfacesare disposed on opposite sides of the cam. Each of the variably slopedcam surfaces is in contact with the cam follower of a corresponding oneof the levers, and each of the variably sloped cam surfaces has a slopewhich varies to counteract variations in a spring force of the spring asthe cam is displaced, thereby maintaining a constant clamping force.

In U.S. Pat. No. 8,646,582 to Bourhill et al., issued 11 Feb. 2014, therail clamp includes a carriage having an actuator frame mounted to itsbase so as to extend upwardly from the base. Springs are mounted in theactuator frame at the upper end of the carriage. An actuator is mountedbetween the base and the springs, and operates on the suspension frameso as to elevate the carriage. A wheel is mounted on a wheel support,and the wheel engages the rail. At least one suspension frame ispivotally mounted to the carriage and at an opposite end, to the wheelsupport. A pair of clamping levers is pivotally mounted to the base ofthe carriage, and the levers are pivotable so as to clamp theirlower-most ends together when their upper ends are moved apart. Brakeshoes mount on the lower-most ends of the levers.

SUMMARY

The presently disclosed retracting rail clamp generally comprises: aload transfer frame rigidly secured to the crane, such as by bolting;and a clamp mechanism suspended within the load transfer frame by atleast one lateral pair of pivotally mounted lift levers, and operablethrough a first and second stage of motion between a raised, brakerelease position, in which the entirety of the rail clamp is disposedsubstantially vertically clear of the rail, and a lowered, brake setposition wherein at least one opposed facing pair of main levers of theclamp mechanism engage the side surfaces of the rail.

The primary forces to be resisted by the rail clamp (e.g. wind load)whilst deployed in the lowered, brake set position act in a directionthat is substantially parallel to the longitudinal orientation of therail. The load transfer frame is accordingly configured internally so asto cradle and provide longitudinal support to the clamp mechanism with aminimal amount of free play in the longitudinal orientation when themechanism is deployed in the lowered brake set position, but also topermit substantially free vertical and lateral translational motion ofthe clamp mechanism within the load transfer frame between the raisedand lowered positions. Unless the specific context requires otherwise,all references in this specification to a “longitudinal” orientationrefer to a direction that is substantially parallel to the longitudinalorientation of the rail; “lateral” orientation refers to a directionthat is substantially perpendicular to the longitudinal orientation ofthe rail.

In some embodiments, the load transfer frame additionally compriseslongitudinally extending internal load transfer beams or braces tofurther enhance longitudinal location of the deployed clamp mechanismwithin the load transfer frame. The load transfer frame may also beconfigured with or comprise chamfered laterally extending internal beamsor braces that cooperate with corresponding chamfers or cam rollers ofthe clamp mechanism so as to laterally center the clamp mechanism withinthe load transfer frame when it is returned to the raised, brake releaseposition.

The clamp mechanism comprises a clamp frame, which includes at least twospaced-apart guide posts connecting an upper frame plate or assemblywith a lower main lever connector plate or assembly. Each of the atleast one pair of lift levers are pivotally mounted on brackets providedat opposing lateral ends of the upper frame plate. The lift leversfurther comprise anti-friction cam rollers at their free ends to enablethe clamp mechanism to “float” with minimum resistance generallyhorizontally in a lateral orientation (i.e. substantially perpendicularto the longitudinal orientation of the rail) within at least onecorresponding lateral pair of opposed facing transverse C-channels, orupon at least one pair of preferably round pegs provided on the loadtransfer frame.

Each of the opposed facing main levers is pivotally mounted to the mainlever connector plate by a pivot disposed between a first, upper end anda second, lower end thereof, such that the lower ends of each opposedfacing pair of main levers clamp together when their upper ends aremoved laterally apart. A brake shoe may be provided on the inner face ofthe lower end of each opposed main lever, and either a bearing (e.g. camroller) or a bearing surface (e.g. cam follower) is provided on theinner face of the upper end of each opposed main lever. One or moreauxiliary return springs may also be provided (either extending directlybetween the upper ends of each of the opposed facing main levers, orcoaxially with the pivot of each main lever) in order to bias the upperends of each of the opposed facing main levers together. The main leverconnector assembly further comprises, or has rigidly affixed to a lowersurface thereof, at least one transverse lateral rail guide. The railguide has a bilateral inwardly angled “double cam” profile dimensionedto produce the necessary side loads to cause the clamp mechanism to movelaterally within the load transfer frame, as may be necessary in orderto accommodate for rail misalignments, and to center the clamp mechanismover the rail as the mechanism is lowered vertically onto the rail andinto the lowered, brake set position. The rail guide may preferably beconstructed of a hardened steel in order to provide a relatively lowcoefficient of friction vis-à-vis the railhead.

A spring plate is slidable along the guide posts of the clamp frame, andis urged in a first, clamping direction by at least one main powerspring disposed between the lower main lever connector assembly and thespring plate. A hydraulically actuated piston is operably connected tothe spring plate, and may be driven under control of an operator byhydraulic pressure in a second, release direction opposite to theclamping direction (i.e. against the biasing force of the power spring)from a hydraulic cylinder operably connected to the upper frameassembly. Suitable low-friction bushings may preferably be providedwithin bores of the spring plate to slidingly accommodate the guideposts.

As described in additional detail below, the spring plate furthercomprises, or has rigidly affixed to a lower surface thereof, a powerwedge cam assembly or a paired cam roller assembly that cooperates withand acts upon either the bearing (in embodiments where a power wedge camis employed) or the bearing surface (in embodiments where a paired camroller assembly is employed) of each of the opposed facing pair of mainlevers as the spring plate moves relative to the clamp frame in eitherthe first, clamping direction or in the second, release direction. Atleast one pair of slotted lift links are pivotally mounted in bracketsat opposing lateral ends of the spring plate, each of which linksextends generally vertically upwards to slidingly engage a pin providedat a selected distance along the elongate body of each corresponding oneof the at least one lateral pair of pivotally mounted lift levers (fromwhich the clamp mechanism is suspended within the load transfer frame).

During the first stage of motion of the rail clamp, relative motionbetween the spring plate and the clamp frame is primarily or entirelyconverted into a generally vertical translation of the clamp mechanismwithin the load transfer frame. As hydraulic pressure within thehydraulic cylinder is reduced to a value below the spring rate of themain power springs, the power springs cause the piston to retreat intothe cylinder and the spring plate to slide along the guide posts in theclamping direction (i.e. away from the lower main lever connector plateand toward the upper frame plate). Since the lift levers are mounted onthe upper frame plate and their corresponding lift links are mounted onthe spring plate, this relative motion between the spring plate andupper frame plate (i.e. the clamp frame) causes a correspondinggenerally vertical upward translational motion of the lift links tooccur vis-à-vis the lift levers. This relative upwards extension of thelift links in turn allows the lift levers to pivot upwards, and theclamp mechanism to lower towards and onto the rail under the force ofgravity. As noted above and further detailed below, if the clampmechanism is not laterally centered over the rail upon initial contacttherewith, the weight of the clamp mechanism acting on the transverserail guide having a bilateral inwardly angled “double cam” profilecauses, in conjunction with the anti-tilt apparatus described below, theclamp mechanism to shift laterally within the load transfer frame as maybe required in order to permit a centered seating of the clamp mechanismon the rail.

The distance at which the pin is located along the elongate length ofeach of the pair of lift levers (measured from the pivotally mounted endof the lift lever towards the free end thereof) determines a lever ratiofor the lift levers. In some preferred embodiments, a roughly 3:1 ratioof lift lever movement is specified, such that the clamp mechanism movesroughly 75 mm vertically for each 25 mm of power spring extension duringthe first stage of motion of the rail clamp. Other lever ratios are ofcourse also possible, and may be selected with reference to the strokeand rate of the power springs, and to the desired vertical clearance ofthe rail clamp (in the brake release position) for a given application.In general, to achieve suitable clamp mechanism lift and lowering whilstminimizing spring force loss in the power springs, a lift lever ratio ofat least 2:1 is desirable.

Once the clamp mechanism has become seated on the rail and no furtherdownward vertical translation of the clamp frame is possible, the mainclamp levers are deployed against the side surfaces of the rail duringthe second stage of motion of the rail clamp until the lowered, brakeset position of the rail clamp has been reached. Although furthervertical translational motion of the clamp frame is prevented by contactwith the rail, relative motion (in either the clamping or releasedirection) between the spring plate and the clamp frame is permitted tocontinue during this second stage of clamp mechanism motion by virtue ofthe freedom of the lift lever pins to travel within the elongate slotsof the slotted lift links.

In embodiments where the spring plate comprises a power wedge cam andthe main levers comprise corresponding cam roller bearings, the relativemotion of the spring plate and clamp frame (during both first and secondstages of motion) causes the bearings of the opposed main levers tocorrespondingly travel along and follow the lateral horizontal profileat each point along the vertical elongate length of the power wedge cam.As the lateral profile of the power wedge cam widens, the upper ends ofthe main levers are correspondingly driven laterally apart. One or moreauxiliary return springs may be provided to bias the upper ends of theopposed facing main levers together in order to maintain contact betweenthe main levers and the power wedge cam when the lateral profile of thepower wedge cam narrows. However, various alternate biasing means formaintaining the lever bearings in rolling contact with the power wedgecam are also possible. For example, each of the main levers may includean auxiliary bracket configured for sliding engagement within avertically extending channel provided on the power wedge cam.

The lateral horizontal profile of the power wedge cam may be varied inwidth and/or slope along its elongate vertical length so as to cause adifferent magnitude of main lever displacement and/or force at differentpoints during the operation of the rail clamp between its raised, brakerelease position and its lowered, brake set position. For example, insome preferred embodiments, the power wedge cam includes a firststraight portion of constant lateral width, and a second generallyfrustoconical portion in which the lateral width of the power wedge camincreases at a constant or increasing rate. In these embodiments, thefirst straight portion corresponds to the first stage of rail clampmotion, such that no main lever displacement is caused while the railclamp is being lowered (or raised up) over the rail, and the secondfrustoconical portion corresponds to the second stage of motion, inwhich vertical translation of the rail clamp has ceased, and in whichthe main levers are driven into engagement with the side surfaces of therail. A variety of suitable constant and/or increasing slopes of thesecond generally frustoconical portion are possible, and may becalculated with reference to the stroke and rate of the power springs ina given application.

Alternate configurations of the lateral horizontal profile of the powerwedge cam are, of course, also possible. For example, in embodimentswhere the main levers are configured for a relatively long stroke,and/or where the width of the rail is small compared to the lateraldistance between the main lever pivots on the lower main lever connectorplate, the first straight portion of the power wedge cam may beabbreviated or eliminated entirely because early commencement of mainlever clamping will not lead to interference between the lower ends ofthe main levers and the rail.

The lateral profile of the power wedge is typically symmetrical aboutits vertical centerline, such that both main levers of each pair aredriven laterally apart (or allowed to draw together) by the samedistance as the power wedge cam translates vertically relative to themain lever bearings. However, in alternate embodiments, such as whererail configuration or other environmental considerations make itdesirable for main lever action to be asymmetrical (i.e. with one of themain levers of a pair travelling a greater distance than the other toreach and clamp onto a rail), the lateral profile of the power wedge cammay be asymmetrical about its vertical centerline.

Similar considerations and variations as outlined above also apply inrelation to embodiments in which the spring plate comprises a paired camroller assembly that cooperates with and acts upon a bearing surfaceprovided on each of the opposed facing pair of main levers. In thesepaired cam roller embodiments, the paired cam rollers rotate about apair of longitudinally oriented axes, and are held in horizontalside-by-side relation and in contact with one another (opposite theirrespective point of contact with the bearing surface of a correspondingmain lever) by at least one bracket that is integral with or rigidlysecured to the lower surface of the spring plate. The paired cam rollersaccordingly rotate in opposite directions during the relative motion ofthe spring plate and clamp frame, and by virtue of being in contact withone another equalize or cancel the lateral compressive forces that maybe created by the action of the paired cam rollers against the bearingsurfaces of the main levers. This results in significant improvements inlowering friction losses, thereby improving force efficiency.

The bearing surfaces of the opposed upper ends of the main levers(and/or the main levers themselves) in these paired cam rollerembodiments are configured so as to angle inwards towards one another,such that the lateral horizontal distance between the bearing surfacesdecreases as the distance from the respective pivot axes about which themain levers pivot increases. Accordingly, as the paired cam rollers movevertically upwards relative to the main levers (and as the main leverscorrespondingly swing laterally outward), a lower attack angle iscreated, which in turn produces a greater mechanical advantage. Inaddition, the vertical extension of the paired cam rollers away from thepivot axes of the main levers creates a longer lever ratio, againincreasing mechanical advantage. The total effect of this combined totalmechanical advantage may accordingly be engineered to compensate forloss of spring force in the main power springs as they extend from acompressed to extended state. As with the power wedge cam embodimentsdescribed above, biasing means such as auxiliary return springs may beemployed to maintain the bearing surfaces of the main levers in constantcontact with the paired cam roller assembly throughout the operationalrange of the rail clamp.

The lateral profile of the bearing surfaces of the opposed main leversmay also include variations analogous to those of the power wedge camembodiments described above, so as to cause desired variations in themagnitude of main lever displacement and/or force at different pointsalong the operation of the rail clamp between its raised and loweredpositions.

To prevent the clamp mechanism from tipping over laterally when contactis made between only one of the bilateral inwardly angled cam surfacesof the rail guide (as may occur when the mechanism is lowered onto anon-centered rail), the clamp mechanism further comprises at least oneform of anti-tilt apparatus that constrains lateral movement of themechanism to substantially vertical and/or substantially lateralhorizontal translational motion. In some embodiments, this anti-tiltapparatus may comprise at least one auxiliary double parallelogramlinkage between the clamp mechanism and the load transfer frame. Inother embodiments, the resolution of any tilting forces acting on theclamp mechanism into substantially vertical and substantially lateralhorizontal components may be achieved by incorporating an intermediatelink assembly, as described below, between the paired lift levers fromwhich the clamp mechanism is suspended within the load transfer frame.

A double parallelogram linkage is known in the art, and generallycomprises a central link body and two pairs of pivotally mountedequal-length arms. The individual arms of the first pair are pivotallymounted to the link body in spaced apart relationship in a first (e.g.horizontal) orientation, and the arms of the second pair are pivotallymounted to the link body in spaced apart relationship in a second (e.g.vertical) orientation that is perpendicular to the first orientation.The free ends of one pair of equal-length arms are pivotally mounted inspaced apart relationship (at the same distance apart as the arms of thepair are connected to the link body) to the clamp mechanism, and thefree ends of the other pair of equal-length arms are pivotally mountedin spaced apart relationship (again at the same distance apart as thearms of the pair are connected to the link body) to the load transferframe. Since the double parallelogram linkage effectively constrainsmotion of the clamp mechanism within the load transfer frame to onlysubstantially vertical and substantially lateral horizontalorientations, the anti-friction cam rollers of the lift levers inembodiments that include a double parallelogram linkage may be supportedby and “float” laterally horizontally upon simple pegs or platesprovided on the load transfer frame without further constraint. Roundpegs are preferred in order to facilitate the self-clearing of anydebris that might accumulate.

In embodiments that employ an intermediate link assembly, theanti-friction cam rollers of the lift levers are constrained within atleast one corresponding lateral pair of opposed facing transverseC-channels that permit free lateral horizontal translation of the camrollers therein, whilst preventing any vertical or longitudinaltranslational motion thereof. An intermediate link pivotally connectsthe paired lift levers, and the pivot axis between the intermediate linkand one lever of the pair is vertically opposite the corresponding pivotaxis between the intermediate link and the second lever of the pairvis-à-vis the main pivot axis of both lift levers on the upper frameplate. For example, if the lift lever/intermediate lever pivot axis of afirst lever is disposed vertically above the main pivot axis, then thelift lever/intermediate lever pivot axis of a second lever will bevertically below the main pivot axis. The intermediate link linkagethereby synchronizes movement as between the lift levers, and incombination with the vertical and longitudinal constraint of the freeends of the paired lift levers by the opposed facing transverseC-channels, motion of the clamp mechanism within the load transfer frameis constrained to only substantially vertical and substantially lateralhorizontal orientations.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and advantages of the disclosedsubject matter, as well as the preferred modes of use thereof, referenceshould be made to the following detailed description, read inconjunction with the accompanying drawings. In the drawings, likereference numerals designate like or similar steps or parts.

FIG. 1 is a vertical cross-sectional view taken along the lateralmidline of a rail clamp according to one embodiment of the presentlydescribed subject matter, showing the rail clamp in the fully raised,brake release position with the clamp mechanism laterally centered overa rail.

FIG. 2 is a cross-sectional view of the rail clamp of FIG. 1, showingthe clamp mechanism in a partially lowered position.

FIG. 3 is a cross-sectional view of the rail clamp of FIG. 1, showingthe clamp mechanism further lowered into contact with the rail.

FIG. 4 is a cross-sectional view of the rail clamp of FIG. 1, showingthe rail clamp in the fully lowered, brake set position.

FIG. 5 is a cross-sectional view of the rail clamp of FIG. 1, showingthe rail clamp in the fully raised, brake release position with theclamp mechanism laterally displaced with respect to a rail.

FIG. 6 is a cross-sectional view of the rail clamp of FIG. 5, showingthe clamp mechanism in a partially lowered position and in initialcontact with the rail.

FIG. 7 is a cross-sectional view of the rail clamp of FIG. 5, showingthe rail clamp in the fully lowered, brake set position with the clampmechanism laterally centered over the rail.

FIG. 8 is a vertical cross-sectional view of the rail clamp of FIG. 1 or5 taken along a lateral plane through the rail clamp and showing adouble parallelogram linkage in accordance with one embodiment of thepresently described subject matter.

FIG. 9 is a perspective view of the double parallelogram linkage of FIG.8.

FIG. 10 is a vertical cross-sectional view taken along the lateralmidline of a rail clamp according to a second embodiment of thepresently described subject matter, showing the rail clamp in the fullyraised, brake release position with the clamp mechanism laterallydisplaced with respect to a rail.

FIG. 11 is a cross-sectional view of the rail clamp of FIG. 10, showingthe clamp mechanism in a partially lowered position and in initialcontact with the rail.

FIG. 12 is a cross-sectional view of the rail clamp of FIG. 10, showingthe clamp mechanism in a further lowered position and laterally centeredover the rail.

FIG. 13a is a cross-sectional view of the rail clamp of FIG. 10, showingthe rail clamp in the fully lowered, brake set position.

FIG. 13b is a diagrammatic view of the rail clamp of FIG. 13a , showingthe rail clamp in the fully lowered, brake set position over astandard-width rail.

FIG. 13c is a diagrammatic view of the rail clamp of FIG. 13a , showingthe rail clamp in the fully lowered, brake set position over anarrow-width rail.

FIG. 14 is an isometric view of the clamp mechanism of FIG. 10 in thefully lowered, brake set position.

FIG. 15 is an isometric view of the rail clamp of FIG. 10 in the fullylowered, brake set position, and showing the external features of theload transfer frame.

FIG. 16 is a vertical cross-sectional view taken along the longitudinalmidline of the rail clamp of FIG. 10 in the fully lowered, brake setposition.

FIG. 17 is an isometric view of the load transfer frame of FIG. 10.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

The following description of preferred embodiments is merely exemplaryin nature and is in no way intended to limit the invention, itsapplication, or uses. The retractable rail clamp of the presentinvention may take form in a number of different embodiments dependingupon the particular requirements of the use, such as the nature, sizeand weight of the rail-mounted machine to be anchored.

With reference to FIGS. 1-9, there is illustrated one embodiment of aretracting rail clamp 100 for braking or anchoring a rail-mountedmachine (not shown) such as a crane. The rail clamp 100 generallycomprises a load transfer frame 102 and a clamp mechanism 104 suspendedwithin the load transfer frame 102 by at least one lateral pair ofpivotally mounted lift levers 106. As will be described further below,clamp mechanism 104 is operable within load transfer frame 102 through afirst and second stage of motion between a raised, brake releaseposition, in which the entirety of the rail clamp 100 is disposedsubstantially vertically clear of a rail 108, and a lowered, brake setposition wherein at least one opposed facing pair of main levers 110 ofthe clamp mechanism 104 engage the side surfaces of the rail 108. Theload transfer frame 102 is adapted for rigid mounting to a rail-mountedmachine by bolting through bores 112.

FIGS. 10-17 illustrate an alternate embodiment of a retracting railclamp 200. As is the case in relation to the embodiment of FIGS. 1-9,rail clamp 200 generally comprises a load transfer frame 202 and a clampmechanism 204 suspended within the load transfer frame 202 by at leastone lateral pair of pivotally mounted lift levers 206, and is operablethrough a first and second stage of motion between a raised, brakerelease position, in which the entirety of the rail clamp 200 isdisposed substantially vertically clear of a rail 208, and a lowered,brake set position wherein at least one opposed facing pair of mainlevers 210 of the clamp mechanism 204 engage the side surfaces of therail 208. The load transfer frame 202 is similarly adapted for rigidmounting to a rail-mounted machine such as by bolting through bores 212.

As is best seen in FIGS. 16 and 17 (illustrated in relation to railclamp 200), the load transfer frame 102 or 202 may additionally compriseone or more longitudinally extending internal load transfer beams orbraces 114, 214 (only 214 is illustrated in relation to rail clamp 200)to enhance longitudinal location of the deployed clamp mechanism 104,204 within the load transfer frame 102, 202, respectively. The loadtransfer frame 102, 202 may also include one or more access ports 116,216 (only 216 is illustrated in relation to rail clamp 200),respectively, to facilitate servicing. In addition, as illustrated inrelation to rail clamp 100, the load transfer frame 102, 202 may also,respectively, be configured with or comprise chamfered laterallyextending internal beams or braces 118, 218 (only 118 is illustrated inrelation to rail clamp 100—see FIG. 1) that cooperate with correspondingchamfers or cam rollers of the clamp mechanism 120, 220 (only 120 isillustrated in relation to rail clamp 100—see FIG. 1) so as to laterallycenter the clamp mechanism 104, 204 within the load transfer frame 102,202 when it is returned to the raised, brake release position.

Rail Clamp 100

In relation to rail clamp 100 of FIGS. 1-9, clamp mechanism 104generally comprises a clamp frame 122 that includes two spaced-apartguide posts 124 connecting an upper frame plate 126 with a lower mainlever connector plate 128. Each of a pair of lift levers 106 ispivotally mounted on brackets 130 provided at opposing lateral ends ofthe upper frame plate 126. The lift levers 106 further compriseanti-friction cam rollers 132 at their respective free ends to enablethe clamp mechanism 104 to “float” with minimum resistance generallyhorizontally in a lateral orientation (i.e. substantially perpendicularto the longitudinal orientation of the rail 108) upon one correspondingpair of preferably round pegs 134 provided on the load transfer frame102.

Each of the opposed facing main levers 110 of clamp mechanism 104 ispivotally mounted to the main lever connector plate 128 by a pivot 136disposed between a first, upper end 138 and a second, lower end 140thereof, such that the lower ends of each opposed facing pair of mainlevers 110 clamp together when their upper ends are moved laterallyapart. A brake shoe (not shown) may be provided on the inner face of thelower end 140 of each opposed main lever 110, and a cam roller bearing142 is provided on the inner face of the upper end 138 of each opposedmain lever 110. One or more auxiliary return springs (not shown) isprovided, either extending directly between the upper ends 138 of eachof the opposed facing main levers 110, or coaxially with the pivot 136of each main lever 110 in order to bias the upper ends 138 of each ofthe opposed facing main levers 110 together. The main lever connectorplate 128 further comprises, or has rigidly affixed to a lower surfacethereof, at least one transverse lateral rail guide 144 (see FIG. 2).The rail guide has a bilateral inwardly angled “double cam” profiledimensioned to produce necessary side loads to cause the clamp mechanism104 to move laterally within the load transfer frame as may be necessaryin order to accommodate for rail misalignments, and to center the clampmechanism 104 over the rail 108 as the mechanism is lowered verticallyonto the rail and into the lowered, brake set position. The rail guide144 may preferably be constructed of a hardened steel in order toprovide a relatively low coefficient of friction vis-à-vis the railhead.

A spring plate 146 is slidable along the guide posts 124 of the clampframe 122, and is urged in a first, clamping direction by a pair of mainpower springs 148, each of which is disposed coaxially with a guide post124 and vertically between the lower main lever connector plate 128 andthe spring plate 146. A hydraulically actuated piston 150 is operablyconnected to the spring plate 146, and may be driven under control of anoperator by hydraulic pressure in a second, release direction oppositeto the clamping direction (i.e. against the biasing force of the powerspring) from a hydraulic cylinder 152 operably connected to the upperframe plate 126. Suitable low-friction bushings (not shown) maypreferably be provided within bores 154 of the spring plate 146 toslidingly accommodate the guide posts 124.

Spring plate 146 further comprises, or has rigidly affixed to a lowersurface thereof, a power wedge cam assembly 156 that cooperates with andacts upon cam roller bearings 142 of each of the opposed facing pair ofmain levers 110 as the spring plate 146 moves relative to the clampframe 122 in either the first, clamping direction or in the second,release direction. At least one pair of slotted lift links 158 arepivotally mounted in brackets 160 at opposing lateral ends of the springplate 146, each of which links 158 extends generally vertically upwardsto slidingly engage a pin 162 provided at a selected distance along theelongate body of each corresponding one of the lateral pair of pivotallymounted lift levers 106 from which the clamp mechanism is suspendedwithin the load transfer frame.

During the first stage of motion of the rail clamp 100, relative motionbetween the spring plate 146 and the clamp frame 122 is primarily orentirely converted into a generally vertical translation of the clampmechanism 104 within the load transfer frame 102. As hydraulic pressurewithin the hydraulic cylinder 152 is reduced to a value below the springrate of the main power springs 148, the power springs 148 cause thepiston 150 to retreat into the cylinder 152 and the spring plate 146 toslide along the guide posts 124 in the clamping direction (i.e. awayfrom the lower main lever connector plate 128 and toward the upper frameplate 126). Since the lift levers 106 are mounted on the upper frameplate 126 and their corresponding lift links 158 are mounted on thespring plate 146, this relative motion between the spring plate 146 andupper frame plate 126 (i.e. the clamp frame 122) causes a correspondinggenerally vertical upward translational motion of the lift links 158 tooccur vis-à-vis the lift levers 106. This relative upwards extension ofthe lift links 158 in turn allows the lift levers 106 to pivot upwards,and the clamp mechanism 104 to lower towards and onto the rail 108 underthe force of gravity. As noted above and further detailed below, if theclamp mechanism 104 is not laterally centered over the rail 108 uponinitial contact therewith, the weight of the clamp mechanism 104 actingon the transverse rail guide 144 having a bilateral inwardly angled“double cam” profile causes, in conjunction with the auxiliary doubleparallelogram linkage 164 described further below (see FIGS. 8 and 9),the clamp mechanism 104 to shift laterally within the load transferframe 102 as may be required in order to permit a centered seating ofthe clamp mechanism 104 on the rail 108.

The distance at which the pin 162 is located along the elongate lengthof each of the pair of lift levers 106 (measured from the pivotallymounted end of the lift lever towards the free end thereof) determines alever ratio for the lift levers 106. A roughly 3:1 ratio of lift levermovement is preferred, such that the clamp mechanism 104 moves roughly75 mm vertically for each 25 mm of power spring 148 extension during thefirst stage of motion of the rail clamp 100.

Once the clamp mechanism 104 has become seated on the rail 108 and nofurther downward vertical translation of the clamp frame 122 ispossible, the main clamp levers 110 are deployed against the sidesurfaces of the rail 108 during the second stage of motion of the railclamp 100 until the lowered, brake set position of the rail clamp 100has been reached. Although further vertical translational motion of theclamp frame 122 is prevented by contact with the rail 108, relativemotion (in either the clamping or release direction) between the springplate 146 and the clamp frame 122 is permitted to continue during thissecond stage of clamp mechanism motion by virtue of the freedom of thelift lever pins 162 to travel within the elongate slots of the slottedlift links 158.

The relative motion of the spring plate 146 and clamp frame 122 (duringboth first and second stages of motion) causes the cam roller bearings142 of the opposed main levers 110 to correspondingly travel along andfollow the lateral horizontal profile at each point along the verticalelongate length of the power wedge cam assembly 156. As the lateralprofile of the power wedge cam 156 widens, the upper ends of the mainlevers 110 are correspondingly driven laterally apart. One or moreauxiliary return springs (not shown) is provided to bias the upper ends138 of the opposed facing main levers 110 together in order to maintaincontact between the main levers 110 and the power wedge cam 156 when thelateral profile of the power wedge cam narrows.

In the embodiment of FIGS. 1-9, the power wedge cam 156 is symmetricalabout its vertical centerline, and includes a first straight portion 166of constant lateral width, and a second generally frustoconical portion168 in which the lateral width of the power wedge cam 156 increases at arelatively constant rate. The first straight portion 166 corresponds tothe first stage of rail clamp 100 motion, such that no main lever 110displacement is caused while the rail clamp 100 is being lowered (orraised up) over the rail 108, and the second frustoconical portion 168corresponds to the second stage of motion, in which vertical translationof the rail clamp 110 has ceased, and in which the main levers 110 aredriven into engagement with the side surfaces of the rail 108.

To prevent the clamp mechanism 104 from tipping over laterally wheninitial contact is made between only one of the bilateral inwardlyangled cam surfaces of the rail guide 144 (as may occur when the clampmechanism is lowered onto a non-centered rail) and the rail 108, theclamp mechanism 104 further comprises at least one auxiliary doubleparallelogram linkage 164 connecting the clamp mechanism 104 and theload transfer frame 102 (see FIGS. 8 and 9). Double parallelogramlinkage 164 generally comprises a central link body 170 and two pairs ofpivotally mounted equal-length arms 172. The individual arms of a firstpair of arms 172 are pivotally mounted to the link body 170 in spacedapart relationship in a first (e.g. horizontal) orientation, and thearms of the second pair of arms 172 are pivotally mounted to the linkbody 170 in spaced apart relationship in a second (e.g. vertical)orientation that is perpendicular to the first orientation. The freeends of one pair of equal-length arms 172 are pivotally mounted inspaced apart relationship (at the same distance apart as the arms of thepair are connected to the link body) to the clamp mechanism 104, and thefree ends of the other pair of equal-length arms are pivotally mountedin spaced apart relationship (again at the same distance apart as thearms of the pair are connected to the link body) to the load transferframe 102. Since the double parallelogram linkage 164 effectivelyconstrains motion of the clamp mechanism 104 within the load transferframe 102 to only substantially vertical and substantially lateralhorizontal orientations, the anti-friction cam rollers 132 of the liftlevers 106 may be supported by and “float” laterally horizontally simplyupon round pegs 134 provided on the load transfer frame 102 withoutfurther constraint.

Rail Clamp 200

In relation to rail clamp 200 of FIGS. 10-17, clamp mechanism 204generally comprises a clamp frame 222 that includes four spaced-apartguide posts 224 (see FIG. 14) connecting an upper frame plate 226 with alower main lever connector assembly 228. A first pair of guide posts 224a connect a first laterally oriented plate 228 a of the main leverconnector assembly 228, and a second pair of guide posts 224 b connect asecond laterally oriented plate 228 b of assembly 228. Plates 228 a and228 b of connector assembly are further connected by longitudinallyoriented plates 228 c and 228 d to form a roughly rectangular connectorassembly 228 for accommodating paired main levers 210.

Each of a pair of lift levers 206 is pivotally mounted on brackets 230provided at opposing lateral ends of the upper frame plate 226. The liftlevers 206 further comprise anti-friction cam rollers 232 at theirrespective free ends to enable the clamp mechanism 204 to “float” withminimum resistance generally horizontally in a lateral orientation (i.e.substantially perpendicular to the longitudinal orientation of the rail208) within a corresponding lateral pair of opposed facing transverseC-channels 234 provided on the load transfer frame 202.

Each of the opposed facing main levers 210 of clamp mechanism 204 ispivotally mounted to the main lever connector plate 228 by a pivot 236disposed between a first, upper end 238 and a second, lower end 240thereof, such that the lower ends of each opposed facing pair of mainlevers 210 clamp together when their upper ends are moved laterallyapart. A brake shoe 241 is provided on the inner face of the lower end240 of each opposed main lever 210, and a cam follower bearing surface242 is provided on the inner face of the upper end of each opposed mainlever. One or more auxiliary return springs (not shown) is provided,either extending directly between the upper ends 238 of each of theopposed facing main levers 210, or coaxially with the pivot 236 of eachmain lever 210 in order to bias the upper ends 238 of each of theopposed facing main levers 210 together. The main lever connectorassembly 228 further comprises, or has rigidly affixed to a lowersurface thereof, at least one transverse lateral rail guide 244. Therail guide has a bilateral inwardly angled “double cam” profiledimensioned to produce necessary side loads to cause the clamp mechanism204 to move laterally within the load transfer frame 202 as may benecessary in order to accommodate for rail misalignments, and to centerthe clamp mechanism 204 over the rail 208 as the mechanism is loweredvertically onto the rail and into the lowered, brake set position. Therail guide 244 may preferably be constructed of a hardened steel inorder to provide a relatively low coefficient of friction vis-à-vis therailhead.

A spring plate 246 is slidable along the guide posts 224 of the clampframe 122, and is urged in a first, clamping direction by a pair of mainpower springs 248, each of which is disposed vertically between thelower main lever connector plate 228 and the spring plate 246. Ahydraulically actuated piston 250 is operably connected to the springplate 246, and may be driven under control of an operator by hydraulicpressure in a second, release direction opposite to the clampingdirection (i.e. against the biasing force of the power spring) from ahydraulic cylinder 252 operably connected to the upper frame plate 226.Suitable low-friction bushings (not shown) may preferably be providedwithin bores 254 of the spring plate 246 to slidingly accommodate theguide posts 224.

Spring plate 246 further comprises, or has rigidly affixed to a lowersurface thereof, a paired cam roller assembly 256 that cooperates withand acts upon the bearing surface 242 of each of the opposed facing pairof main levers as the spring plate 246 moves relative to the clamp frame222 in either the first, clamping direction or in the second, releasedirection. The paired cam rollers 257 of assembly 256 rotate about apair of longitudinally oriented axes, and are held in horizontalside-by-side relation and in contact with one another (opposite theirrespective point of contact with the bearing surface 242 of acorresponding main lever 210) by at least one bracket 259 that isintegral with or rigidly secured to the lower surface of the springplate 246. The paired cam rollers 257 accordingly rotate in oppositedirections during the relative motion of the spring plate 246 and clampframe 222, and by virtue of being in contact with one another, equalizeor cancel the lateral horizontal compressive forces that may be createdby the action of the paired cam rollers 257 against the bearing surfaces242 of the main levers 210. Each one of the pair of cam rollers 257rotates against the other, and against the bearing surface 242 of itsassociated main lever 210 in pure rolling motion. This cancellation ofthe lateral horizontal compressive forces acting on paired cam rollers257 means that the axles and bearings of cam rollers 257 are notsubjected to high forces, which permits the use of smaller cam rolleraxles and/or anti-friction roller bearings (as opposed to plainbearings), and in turn results in a low friction and more efficientmechanism.

At least one pair of slotted lift links 258 are pivotally mounted inbrackets 260 at opposing lateral ends of the spring plate 246, each ofwhich links 258 extends generally vertically upwards to slidingly engagea pin 262 provided at a selected distance along the elongate body ofeach corresponding one of the lateral pair of pivotally mounted liftlevers 206 from which the clamp mechanism is suspended within the loadtransfer frame.

During the first stage of motion of the rail clamp 200, relative motionbetween the spring plate 246 and the clamp frame 222 is primarily orentirely converted into a generally vertical translation of the clampmechanism 204 within the load transfer frame 202. As hydraulic pressurewithin the hydraulic cylinder 252 is reduced to a value below the springrate of the main power springs 248, the power springs 248 cause thepiston 250 to retreat into the cylinder 252 and the spring plate 246 toslide along the guide posts 224 in the clamping direction (i.e. awayfrom the lower main lever connector plate 228 and toward the upper frameplate 226). Since the lift levers 206 are mounted on the upper frameplate 226 and their corresponding lift links 258 are mounted on thespring plate 246, this relative motion between the spring plate 246 andupper frame plate 226 (i.e. the clamp frame 222) causes a correspondinggenerally vertical upward translational motion of the lift links 258 tooccur vis-à-vis the lift levers 206. This relative upwards extension ofthe lift links 258 in turn allows the lift levers 206 to pivot upwards,and the clamp mechanism 204 to lower towards and onto the rail 208 underthe force of gravity. As noted above and further detailed below, if theclamp mechanism 204 is not laterally centered over the rail 208 uponinitial contact therewith, the weight of the clamp mechanism 204 actingon the transverse rail guide 244 having a bilateral inwardly angled“double cam” profile causes, in conjunction with the intermediate linkassembly 264 described further below (see FIGS. 11 and 14) between thepaired lift levers 206, the clamp mechanism 204 to shift laterallywithin the load transfer frame 202 as may be required in order to permita centered seating of the clamp mechanism 204 on the rail 208.

The distance at which the pin 262 is located along the elongate lengthof each of the pair of lift levers 206 (measured from the pivotallymounted end of the lift lever towards the free end thereof) determines alever ratio for the lift levers 206. A roughly 3:1 ratio of lift levermovement is preferred, such that the clamp mechanism 204 moves roughly75 mm vertically for each 25 mm of power spring 248 extension during thefirst stage of motion of the rail clamp 200. In general, to achievesuitable clamp mechanism lift and lowering whilst minimizing springforce loss in the power springs, a lift lever ratio of at least 2:1 isdesirable.

Once the clamp mechanism 204 has become seated on the rail 208 and nofurther downward vertical translation of the clamp frame 222 ispossible, the lower ends of main clamp levers 210 are deployed againstthe side surfaces of the rail 208 during the second stage of motion ofthe rail clamp 200 until the lowered, brake set position of the railclamp 200 has been reached. Although further vertical translationalmotion of the clamp frame 222 is prevented by contact with the rail 208,relative motion (in either the clamping or release direction) betweenthe spring plate 246 and the clamp frame 222 is permitted to continueduring this second stage of clamp mechanism motion by virtue of thefreedom of the lift lever pins 262 to travel within the elongate slotsof the slotted lift links 258.

The relative motion of the spring plate 246 and clamp frame 222 (duringboth first and second stages of motion) causes the paired cam rollers257 of assembly 256 into corresponding translational motion vis-à-visthe bearing surfaces 242. The bearing surfaces 242 of the opposed upperends of the main levers 210 (and/or the upper ends of the main leversthemselves) are configured so as to angle inwards towards one another,such that the lateral horizontal distance between the bearing surfaces242 decreases as the distance from the respective pivot axes 236 aboutwhich the main levers 210 pivot increases. Accordingly, as the pairedcam rollers 257 move vertically upwards relative to the main levers 210(and as the main levers correspondingly swing laterally outward), theupper ends 238 of the main levers 210 are driven laterally apart, and alower attack angle “a” is created, which in turn produces a greatermechanical advantage. In addition, the vertical extension of the pairedcam rollers 257 away from the pivot axes 236 of the main levers 210creates a longer lever ratio “Le”, again increasing mechanicaladvantage. One or more auxiliary return springs (not shown) is providedto bias the upper ends 238 of the opposed facing main levers 210together in order to maintain the bearing surfaces 242 of the mainlevers 210 in constant contact with the paired cam rollers 257throughout the operational range of the rail clamp 200.

The lower ends 240 of main levers 210 (i.e. the “jaws” of the railclamp) must be able accommodate varying rail widths, as well as somewear of brake shoes 241, and this requires main levers 210 to rotate tovarying positions, depending primarily on rail width. FIG. 13billustrates the attack angle “a” and lever ratio “Le” of rail clamp 200in the fully lowered, brake set position over a standard-width rail, andFIG. 13c illustrates the attack angle “a” and lever ratio “Le” of railclamp 200 in the fully lowered, brake set position over a narrow-widthrail.

As any spring (including main power spring 248) extends, it loses forceaccording to its spring rate. Accordingly, in the absence of springcompensation, rail clamp 200 would lose capacity on narrower rails ascompared to standard-width rails (or with shoe wear). As noted above, inrail clamp 200, spring force is multiplied by attack angle “α” of theinclined plane that is created by the inwardly angled configuration ofbearing surfaces 242 of the opposed upper ends of the main levers 210,and also by lever ratio “Le”, which is variable depending on springextension. As the lower ends 240 of main levers 210 rotate toaccommodate narrower rails or worn shoes, the effective cam attack angle“α” is reduced. This results in a lower angle inclined plane relative tothe paired cam rollers 257, thereby increasing mechanical advantage withresultant force multiplication. Furthermore, as the paired cam rollers257 move vertically upwards relative to the main levers 210, so does theroller contact point of the cams. This produces a lengthened lever arm“Le” and a correspondingly increased lever ratio for the main levers210. The combination of these two characteristics results in an overallincreased mechanical advantage for the clamp mechanism 204 as the mainpower springs 248 extend. By matching the mechanism characteristics,such as initial cam angle and lever length with spring rate, themechanism can thereby provide substantially effective compensation forspring force loss.

To prevent the clamp mechanism 204 from tipping over laterally wheninitial contact is made between only one of the bilateral inwardlyangled cam surfaces of the rail guide 244 (as may occur when the clampmechanism is lowered onto a non-centered rail), the clamp mechanism 204further comprises an intermediate link assembly 264 between the pairedlift levers 206. As noted above, the lift levers 206 compriseanti-friction cam rollers 232 at their respective free ends to enablethe clamp mechanism 204 to “float” with minimum resistance generallyhorizontally in a lateral orientation (i.e. substantially perpendicularto the longitudinal orientation of the rail 208) within a correspondinglateral pair of opposed facing transverse C-channels 234 provided on theload transfer frame 202. An intermediate link 264 pivotally connects thepaired lift levers 206, and the pivot axis between the intermediate linkand one lever of the pair is vertically opposite the corresponding pivotaxis between the intermediate link and the second lever of the pairvis-à-vis the main pivot axis of both lift levers on the upper frameplate 226. For example, if the lift lever/intermediate lever pivot axisof a first lever is disposed vertically above the main pivot axis, thenthe lift lever/intermediate lever pivot axis of a second lever will bevertically below the main pivot axis. The intermediate link linkagethereby synchronizes movement as between the lift levers 206, and incombination with the vertical and longitudinal constraint of the freeends of the paired lift levers by the opposed facing transverseC-channels 234, motion of the clamp mechanism 204 within the loadtransfer frame 202 is constrained to only substantially vertical andsubstantially lateral horizontal orientations.

The present description is of the best presently contemplated mode ofcarrying out the subject matter disclosed herein. The description ismade for the purpose of illustrating the general principles of thesubject matter and not to be taken in a limiting sense; the describedsubject matter can find utility in a variety of implementations withoutdeparting from the scope of the invention made, as will be apparent tothose of skill in the art from an understanding of the principles thatunderlie the invention.

We claim:
 1. A retracting rail clamp for braking or anchoring arail-mounted machine by clamping opposite sides of a longitudinal railmember, the rail clamp comprising a load transfer frame rigidly securedto the machine; and a clamp mechanism comprising a clamp frame includingat least two spaced-apart guide posts connecting an upper frame plate orassembly with a lower main lever connector plate or assembly, whereinsaid clamp mechanism is suspended within said load transfer frame by atleast one lateral pair of pivotally mounted lift levers, and operablebetween a raised, brake release position and a lowered, brake setposition wherein at least one opposed facing pair of main levers of theclamp mechanism engage the side surfaces of the rail.
 2. The rail clampof claim 1, wherein the at least one pair of lift levers are pivotallymounted on brackets provided at opposing lateral ends of the upper frameplate, said lift levers further comprising anti-friction cam rollers attheir free ends to enable the clamp mechanism to float with minimumresistance generally horizontally in a lateral orientation,substantially perpendicular to the longitudinal orientation of the rail,within at least one corresponding lateral pair of opposed facingtransverse C-channels or upon at least one pair of pegs provided on theload transfer frame.
 3. The rail clamp of claim 1, further comprising asingle hydraulic cylinder for operation of the rail clamp between theraised, brake release position and the lowered, brake set position. 4.The rail clamp of claim 1, wherein both the load transfer frame and theclamp mechanism are completely retracted from the rail member when inthe raised, brake release position to accommodate wide variation in railheight and rail float.
 5. The rail clamp of claim 1, wherein the liftlever ratio is greater than 2:1.
 6. The rail clamp of claim 1, whereinat least one pair of slotted lift links are pivotally mounted inbrackets at opposing lateral ends of a spring plate, each of which liftlinks slidingly engaging a pin provided at a selected distance along theelongate body of each corresponding one of the at least one lateral pairof pivotally mounted lift levers.
 7. The rail clamp of claim 2, furthercomprising an intermediate synchronizing linkage between the at leastone pair of lift levers and constraining motion of the clamp mechanismto only substantially vertical and substantially lateral horizontalorientations vis-à-vis the load transfer frame.
 8. The rail clamp ofclaim 1, further comprising paired cam rollers in contact with oneother.
 9. The rail clamp of claim 8, wherein the paired cam rollerscontact lever-borne cams arranged such that the inclined plane anglesdecrease and resultant mechanical advantage increases as the clamp isextended from the raised, brake release position to the lowered, brakeset position.
 10. The rail clamp of claim 1, further comprising a railguide having a bilateral inwardly angled double cam profile forcentering the clamp mechanism over the rail as the mechanism is loweredvertically onto the rail and into the lowered, brake set position. 11.The rail clamp of claim 1, wherein the load transfer frame compriseschamfered laterally extending internal beams or braces to laterallycenter the clamp mechanism within the load transfer frame when it isreturned to the raised, brake release position.